Weathering and erosion processes are directly affected by the presence and activity of biota. Plants as main terrestrial primary producers control water, carbon and nutrient cycles throughout the critical zone. The interaction between plant roots, microbes and soil minerals that occur in the rhizosphere determine the rate of surface and deep weathering. Plants roots and the symbiotic organisms such as mycorrhizal fungi associated with organic acids and chelates attack primary minerals to release mineral nutrients and associated elements like Si and Al. As a result of weathering Al and Fe can be released to solution becoming bioavailable or they can be captured (organo-metal complexes) or precipitated as a secondary mineral. The present proposal will determine the direct (i.e. uptake) and indirect (i.e. exudates) contribution of biota (i.e. plants and microorganisms) to the mobilization and precipitation of iron and aluminium as secondary faces in the saprolite-saprock interface. Through this investigation we seek to understand and quantify the enhancement of weathering processes by the joint actions of plants and the microbes at the weathering front (saprock) ant to determine the potential contribution of this process to carbon stabilization in the deep regolith. Specifically, we intent to determine the direct effect of plant and microbial uptake, and the indirect effect of dissolve organic matter and soil microbial activity in mineral dissolution and precipitation of Fe and Al secondary minerals. We have planned to address our objectives using two independent approaches. In our first approximation we will fully characterize the distribution of secondary mineral phases and organic matter moieties in the soil-saprolite-saprock interface along a vegetation gradient in the Chilean coastal cordillera (27o to 40oS) using study sites that has been previously characterized. In our second approach we will determine of the role of plants and microbes using a bioreactor column experiment. This columns will be filled with fresh saprock samples collected in one of the sites. In this experiment we will manipulate the contribution of different biotic agents (plants, microbes, DOM). The effect of each biogenic agent will be independently quantified. In relation to the results that will be obtained, it is expected to obtain a complete biogeochemical characterization of the distribution and patterns of Fe and Al secondary minerals and DOM along the vegetation and climatic gradient. It is expected that these sites will display different DOM characteristics and compositions of oxides and hydroxides of Fe and Al. We expect that the desert ecosystem because of their lower primary productivity will present less developed soils, which will reduce weathering processes and mobility of Fe and Al, which will be still contain in primary phases and mostly Fe crystalline secondary oxides. Therefore, the mineral structures in this drier climate will have a higher degree of crystallinity but lower content of secondary minerals in depth. On the contrary, in more humid areas higher primary productivity and higher DOM influx to soil will enhance microbial activity and weathering in the deep regolith. It is expected that this soils will display a larger accumulation of Al oxy-hydroxides minerals like gibbsite and minerals of short-range order. Complementary, the bioreactor experiment will allow direct quantification of biogenic weathering and to determine the role of dissolve organic matter fueling microbial activity and weathering process during saprock weathering. The study of Fe and Al mobility and precipitation dynamics and their relation with dissolve organic matter along this climatic gradient and the discrimination of direct and indirect biotic controls on mineral weathering will greatly improve our understanding of the mechanism for carbon cycling and stabilization and its relation with Fe and Al biotic cycling in the deep regolith.